Sc(OTf)3-catalyzed Cyclooligomerization of 2,4-Dialkoxybenzyl Alcohols. Formation of Resorcin[n]arene Peralkyl Ethers

Summary The cyclooligomerization of 2,4-dialkoxybenzyl alcohols 3 catalyzed by Sc(OTf)₃ in CH₃CN under high dilution conditions produced a series of resorcin[n]arene peralkyl ethers containing four to nine resorcinol units. When the reactions were conducted at 50°C, the cyclic tetramers 4, which are thermodynamically favored products, are selectively formed in good yields. It is noteworthy that the reaction of 2,4-dimethoxybenzyl alcohol 3d at 0°C produced the corresponding cyclic octamer 8d as the major product. In other cases, such as the selective formation of a cyclic octamer could not be observed. This selective formation of 8d is due to a combination of the reversibility of the oligomerization in the presence of 3d and the insolubility of the octamer in the reaction medium. The conformational analysis of these cyclic oligomers was done by variable temperature ¹H NMR spectroscopy.